I'm not informed on the topic by any means, but my take is reddit should be less susceptible because they have the resources to combat bots and spam -- or at least empower mods to do so -- but they choose not to. It's pretty surprising to me that they cut support for critical mod tools like Pushshift without having a replacement ready to go. The mod support posts only spoke of tools/capabilities they were planning or committing to, or links to "we want to help" pages. Lemmy is probably more susceptible to bots, especially now, but I think a lot of that up-to-date expertise of how to spot bots is coming over with the new wave of membership. Plus, I don't know if or how bots would be worth it here aside from trolling.

tl;dr I have no idea